Download a windowed selection from dap.geosoft.com or directly into your Geosoft application via Seeker. As with DAP's SRTM US Elevation 30m dataset, the new SRTM grids are provided in Geosoft Grid format.
USGS EarthExplorer hosts worldwide coverage of void filled data and provides open distribution of this high-resolution global dataset. This service offers SRTM data as 1-degree tiles with a regularly spaced grid of elevation points in three formats: Digital Terrain Elevation Data (DTED®), Band interleaved by line (BIL), and Georeferenced Tagged Image File Format (GeoTIFF).
Episode 4 of the Top 5 Inversion Best Practice web series is now available, and it focuses on understanding magnetization vector inversion results. Many of you have been using this method on new and historical magnetic field data to uncover the subsurface in a whole new way – adding additional perspective to your interpretations.
Watch episode 4 and learn about:
The scalar components of the magnetization vector and how they’re related
The representation of the magnetization vector in both Cartesian and rotated coordinate systems
Why IRI is important and how to best interpret your magnetic field data with MVI
In Geochemistry, there are a number of tools that run on all, displayed, or a selection of assay channels.
If your assay channels are not identified here are some tips on how to update the channel attributes.
Identify Assay Channels
The assay channels need to be identified with an ASSAY "class" in the channel attributes. If your fields are not being identified automatically, you can fix this during or after importing your sample results.
1. Identify assay channels during import
If the column header name is a member of the periodic table of the elements, such as "Cu" (or "cu", as this test is not case-sensitive) then it will be labelled as an Assay.
For more complex cases, such as oxides, you can add to the assaylist.csv (find this file in C:\Program Files (x86)\Geosoft\Oasis montaj\user\csv\assaylist.csv).
You can add the field names directly to the list: MnO2 FeO
Or items can contain * and ? to match multiple or single characters: *(ppb) *_PPM *_pp?
2. Identify assay channels in an existing database
If the channels are already in a database, you can use GeochemImport > Assay Attributes > Set Attributes to assign the ASSAY class. Choose the fields that need to be identified as Assays and the class will be attached to the channel attributes.
Update Channel Labels
You can update the Labels for the assay channels as well. Labels appear in reports and symbol legends so that a channel named "FEO2_PPM_" can have a label that says "FeO2 (ppm)"
Export the current attributes using GeochemImport > Assay Attributes > Export Attributes
Edit the CSV file. You can make the edits in a simple text editor like Notepad. Be sure to re-save it as a CSV file if you edit it in Excel.
Import the updated attributes to the database using GeochemImport > Assay Attributes > Import Attributes.
Save your assay attribute table in a safe place so it can be re-used on other projects will similar imported assay fields.
There are several ways to view statistics of your database or channel values. Here are three that I often use:
1. Channel Stats. Click twice on the channel name to highlight the current line (or drillhole); click three times to include all the selected lines in the database. Then right click to access "Statistics".
The same information can be accessed via Database Tools > Report > Mark Statistics. This menu has Line/Channel Report and Total Distance too!
2. Advanced Statistics are available in some extensions. Look in Database Tools > Geostatistics Toolkit > Summary Statistics.
In the Geochemistry menu, this is found under GeochemAnalysis > Summary Statistics.
3. Another option in GeochemAnalysis > Save Statistics will save stats for all channels directly to a CSV file.
When an XML file is automatically created along with a database, grid, voxel or map, you can be sure that it contains some useful information, with ISO 19115 standard tags, that can tell you who, where, and how the data was created.
The Project Name field is automatically populated with the path and name of the Geosoft Project File (*.GPF) where the dataset was created. Since the folders in the path often are related the to the data, this can be useful information for when the dataset is moved around to other file systems and servers.
The name of the data creator and the date are also recorded.
Coordinate System information is available and is always synchronized with the Coordinate System of the dataset.
"How" the dataset was created is often captured in the Lineage section. This can be used to easily identify a subset database or the type of gridding or filter that was used on a grid or voxel.
No harm will come from deleting these small text files, but if you keep them they may become a valuable reference to you when you need them.
Whether you're new to inversion modelling, or have been doing it for years – you already understand why constraints are so important (watch our introductory video for a quick recap). There are many new features in Oasis montaj, like wireframing and drillhole tools that can help build constraints for your inversions. There are also constraints available in VOXI that you can't easily find anywhere else, like gradient reference models. Based on common questions from our users, episode 3 of the web series is a guide to the most impactful constraints and how to implement them in VOXI to improve your inversion results.
In this episode you'll learn how upper and lower bounds, and reference and weighting models work. You'll also find tips on when to use them and see an example of how they can dramatically improve your inversion results.
Geosoft released VOXI two years ago, and since then geophysicists around the globe have run over 11,000 gravity and magnetic inversions using the service. These airborne and ground geophysical surveys are often accompanied by drillhole investigations as well. When it comes to inversion, additional information can constrain your model and improve your result.
Many of you are interested in incorporating susceptibility and/or density measurements from core samples but were stumped on how to build the VOXI constraint. In response to your requests, Oasis montaj 8.2 now has a simple model builder used to create parameter reference and weighting voxels from a drillhole database.
There are some important things to consider when using core measurements as constraints in inversion. For example, it is important that a background is removed from the core data so that it is consistent with the relative-to-background rock properties in the inversion result. Also, there shouldn't be an expectation that the constraint will yield a result that matches the core measurements exactly. After all, a 50x50x50m cell in the 3D model has a volume that is 1.6 million times larger than a 50m-long diamond drillhole core sample! It is far more valuable to expect the drillhole constraint to influence the relative distribution of the rock property within the model volume.
The new tool can be found in Oasis montaj 8.2 - watch the how-to video below.